There is substantial evidence that the pathogenesis of Alzheimer's Disease (AD) may involve mitochondrial dysfunction and oxidative damage. Mitochondrial dysfunction could occur as either a consequence of primary genetic mutations or due to acquired mitochondrial DNA (mtDNA) mutations, which may be related to oxidative damage. In the present proposal, we will examine whether there is an increased incidence of mtDNA mutations in postmortem brain tissue from AD patients as compared to normal controls. We will utilize direct mtDNA sequencing as well as denaturing gelelectrophoresis to detect low frequency mutations, and we will correlate levels of 8-hydroxy-2- deoxyguanosine (OH8dG), a marker of oxidative damage to DNA. We have developed a sensitive and accurate assay for OH8dG, which is useful in examining concentrations in body fluids. We intend to utilize this assay to measure OH8dG in urine, plasma and CSF of AD patients and controls. We will make cybrids utilizing platelets obtained from well characterized AD patients. *-amyloid deposition may cause oxidative stress and/or oxidative stress may increase -amyloid production. We will examine whether transgenic mice with the APP V717F mutation have increased mtDNA mutations as assessed by direct sequencing. We will correlate this with concentrations of b-amyloid as measured by ELISA, as well as markers of oxidative damage including malondialdehyde, OH8dG and 5-nitro-gamma-tocopherol. We will examine transgenic mouse lines which are deficient in the mitochondrial free radical scavenging enzyme manganese superoxide dismutase. We will also utilize mice, which are deficient in glutathione peroxidase, which detoxifies hydrogen peroxide within mitochondria. We will determine whether these mice develop age-dependent increases in oxidative damage within mtDNA, increased numbers of mtDNA mutations and whether this correlates with increases in extractable levels of b-amyloid. These studies are designed to help to further elucidate the role of mitochondrial dysfunction and oxidative damage in normal aging and AD.